A strain wave gearing is composed of three members: a rigid internally toothed gear, a flexible externally toothed gear, and a wave generator. A unitary strain wave gearing with an output flange linked with an externally toothed gear is described in Patent Document 1. A flat-profile strain wave gearing used as a reducing mechanism that is fitted onto a motor shaft of an electric motor is described in Patent Document 2. The motor shaft is linked with the wave generator in the flat-design strain wave gearing, and the motor shaft is rotatably supported by a support bearing.
The strain wave gearings disclosed in Patent Document 1 and 2 are typically fitted by the user. The wave generator attached to the motor shaft is assembled on the inside of the externally toothed gear fitted to the inside of the internally toothed gear. Axial positioning of the assembled wave generator and other work is necessary.
A unitary strain wave gearing in which the three members are formed integrally in advance is proposed in Patent Document 3. According to Patent Document 3, the input shaft of the wave generator is supported by the internally toothed gear via a support bearing. The internally toothed gear and externally toothed gear are linked together by a linking member so as to allow relative rotation therebetween, and prevent any deviation from the central axis direction. Since the central-axis position of the wave generator is restricted by the support bearing in a unitary strain wave gearing, the wave generator does not need to be axially positioned as a part of the work performed to attach the wave generator to the motor shaft.